Interleukin 4 (IL-4) is a potent immunoregulatory cytokine with extremely diverse effects on a number of target cells. IL-4 plays an important physiologic role in hematopoietic cell growth and differentiation, tumor surveillance and local protective inflammatory responses. However, dysregulated IL-4 production has been shown to have extremely detrimental effects. Pathological conditions such as atopic disease and inability to resolve certain parasitic infections are clearly associated with overproduction of IL-4. IL-4 was originally defined as a T cell cytokine, but it is now clear that mast cells are also important IL-4 producing cells. Mast cells are widely distributed in vascularized tissues in the proximity of many IL-4 target cells. This location provides the opportunity for mast cell-derived IL-4 to easily access such cells and effectively modulate a wide range of local inflammatory responses. Because of the unique tissue distribution of mast cells and thus potentially distinct functions of mast cell-derived IL-4 on local inflammatory responses, it was predicted that mechanisms which regulate IL-4 gene expression in mast cells would differ from those in T cells. Recent studies have confirmed this prediction. It was demonstrated that there are unique cis acting sequences which regulate IL-4 gene transcription in T and mast cells. A major component of tissue-specific transcriptional activity in mast cells appears to be contained in a sequence in the second intron of the IL-4 gene. This sequence exhibits prototypic enhancer activity in mast cell lines and its activity is dependent on the interaction of both positive and negative regulatory elements. The specific aims of this proposal are: 1. To identify essential positive and negative acting-sequences that comprise the IL-4 intronic enhancer. 2. To identify DNA binding proteins which specifically govern the function of the IL-4 intronic enhancer and determine their expression and binding dynamics in mast cells and cells of other lineages. 3. To examine populations of freshly isolated mast cells for their ability to express IL-4 upon stimulation and analyze the expression of mast cell specific transcription factors in these cells. 4. To determine how the IL-4 intronic enhancer interacts with other IL-4 regulatory sequences to modulate IL-4 expression in mast cells. DNA- protein binding assays and response element-reporter gene constructs in concert with transient transfection assays will be used to accomplish these aims. Understanding the molecular basis for tissue specific regulation in mast cells is an important first step in ultimately devising therapeutic strategies for selectively limiting or augmenting mast cell or T cell-derived IL-4 activity in allergic disease or immunotherapy of tumors such as melanoma.